AN-D17

Supertex inc.
AN-D17
Application Note
High Voltage Off-Line Linear Regulator
by Jimes Lei, Applications Engineering Manager
Introduction
to minimize the loading on batteries, especially when the vehicles are not in use for long periods of time. For example,
only a few microamperes are needed for powering memory
ICs. In such situations the quiescent current of the regulator
should be within a few microamperes.
There are many applications for small, linear voltage regulators that operate from high input voltages. They are ideally
suited for powering CMOS ICs, small analog circuits, and
other loads requiring low current. These circuits can be used
in several applications requiring power directly from the utility line. They can also be used for applications which either
have very wide input voltage variations or environments with
high voltage spikes; for example, telecommunications, automotive, and avionics. This application note discusses several circuits which will benefit these applications.
The high voltage protected, 5.0V linear regulator shown in
Figure 1 meets all of the above requirements. It is very simple, compact and inexpensive. The high operating voltage
and high transient voltage protection are achieved by using
Supertex part #LND150N8 in conjunction with a 5.0V linear
regulator, Ricoh part #RH5RA50AA.
Direct off-line applications require operation at 120VAC to
240VAC which corresponds to maximum peak voltages of
±340V. Applications in telecommunications, automotive, and
avionics require immunity against very fast, high voltage transients. In telecommunications, the high voltage transients
are caused by lightning or spurious radiations. In automotive
and avionics they are caused by inductive loads such as
ignition coils and electrical motors. International Standards
Organization specification ISO/TR7637, for electrical interference by conduction and coupling in automobiles, shows
that transients up to -300V and +120V can be generated due
to various inductive loads.
Circuit Description
The LND150N8 is a 500V, N-channel, depletion-mode
MOSFET. It has a maximum RDS(ON) of 1.0KΩ, VGS(OFF) of
-1.0 to -3.0V, and an IDSS of 1.0 to 3.0mA. The RH5RA50AA
is a 5.0V ±2.5% voltage regulator with a maximum quiescent
current of 1.0µamp. Both these parts are available in the
SOT-89 (TO-243AA) surface mount package.
The high voltage input, HVIN, is connected to the anode of diode D. The cathode of the diode is connected to the drain of
the LND1. The diode is used as protection against negative
transient voltages and as a half-wave rectifier for off-line application. The LND1 is connected in the source follower configuration, with its gate connected to the output, VOUT, and
its source to the input ofthe 5.0V regulator, VIN. Capacitors
C1, C2 and C3 are bypass capacitors. C3 is required when
HVIN is negative, such as during the negative half cycle of
an AC line, or negative transients. The proper value of C3 is
chosen based on the worst case duration and duty cycle of
the negative pulses on HVIN.
In addition to the ability to withstand high voltages, many circuits used for the above mentioned applications also require
low quiescent current. The low quiescent current is required
to minimize power dissipation in these linear regulators.
Many telecommunication applications require very low quiescent current because there are limitations to the allowable
current that can be drawn from the telephone lines. Automotive and avionics applications require low quiescent current
Figure 1: High Voltage Universal Off-Line Linear Regulator
HVIN
IN4005
D
LND150N8
C3
C2
0.01μF
Supertex inc.
+
VGS
RH5RA50AA
VOUT = 5.0V
C1
0.01μF
RL
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
1
AN-D17
HVIN, VIN and VOUT are at 0V before a voltage is applied to
HVIN. The LND1 is turned on when its gate-to-source voltage, VGS = 0V. Once a voltage is applied to HVIN, current
will flow through the diode and the “normally on” channel
of the LND1 charging capacitor C2. The voltage across C2
is connected to VIN. As VIN starts to increase, VOUT will also
continue to increase until it reaches its regulated voltage of
5.0V.
The LND1 is configured as a source follower with its gate
connected to a fixed 5.0V value (nominal). The voltage on
the source, VIN, will follow the voltage on its gate, minus VGS.
VIN = VOUT -VGS where VGS is the voltage required to supply
the input current IIN. If 500VDC is applied on HVIN, VOUT will
remain at 5.0V and VIN should be between 6.0 to 8.0V, since
VGS(OFF) of LND150N8 is guaranteed to be -1.0 to -3.0V. The
actual observed value was 6.26V.
The dropout voltage, (VIN -VOUT), for the 5.0V regulator with
a 1.0mA load is rated as 30mV. To maintain regulation, VIN
must be equal to or greater than 5.03V. As IIN increases, VIN
decreases and thereby increases the gate-to-source voltage
on the LND1 to meet the IIN requirement. The transfer characteristics of the LND1 give a good indication of VGS vs. IIN.
DC Operation
The LND1 increases the maximum operating voltage range
from 13.5 to 500VDC. In order for the output to maintain regulation, the voltage difference (VIN -VOUT), must be greater
than the regulator’s specified dropout voltage of 30mV at
1.0mA load current. The measurements are shown below:
HVIN
IIN
VIN
VOUT
Conditions
10 to 500V
770nA
6.26V
5.02V
No load
10 to 500V
503µA
5.56V
5.02V
10KΩ
10 to 500V
1.0mA
5.30V
5.02V
5.0KΩ
Since the LND150N8 is connected in a source follower configuration, the value of VIN can be estimated as shown in
Figure 2.
Figure 2: VIN Calculation
HVIN
D
ID
G
VOUT
S
Advantages of the LND1
The important parameters of the LND1 are its 500V breakdown voltage, 1.5pF output capacitance and 1.0MΩ dynamic output impedance. Supertex utilizes a proprietary design
and fabrication process to achieve very flat output characteristics which gives this device its very high dynamic impedance, rO. The RH5RA50AA has an absolute maximum
input voltage rating of 13.5V. The highbreakdown voltage
of the LND1 extends the maximum input operating voltage
range from 13.5V to 500V. The low output capacitance and
high dynamic impedance prevent the input voltage of the
RH5RA50AA from exceeding its absolute maximum value
of 13.5V when very fast high voltage transients are present.
The ripple rejection ratio is also improved by several orders
of magnitude.
C2
VIN
ID = IDSS • (1 - VGS / VGS(OFF) )2
VGS = VOUT - VIN
VIN = VOUT - VGS(OFF) • (1 - √ID / IDSS )
High Voltage Transient Protection
Positive and negative transient voltages were applied on
HVIN. The positive transient voltages are blocked by the
LND1 and the negative transient voltages are blocked by
the 1N4005 diode, which has a 600V PIV rating.
LND1 improves the performance of the 5.0V linear regulator
in the areas listed below. Observations and measurements
were taken under three different loading conditions: no load,
10KΩ, and 5.0KΩ.
a) DC operation extended from 13.5 to 500V
b) High voltage transient protection
c) Greatly improved ripple rejection ratio
d) Eliminates power-up transients
Supertex inc.
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
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AN-D17
Figure 3: Positive Transient Test Condition
HVIN
Figure 5: Estimate VIN Increase Due to Transients
VIN
C2
0.01μF
ID
HVIN
LND1
VOUT
REG
C1
0.01μF
CDS
1.5pF
Ro
5kΩ
C2
0.01µF
50msec
310V
HVIN
rO = AC resistance, typically 1.0MΩ
(almost no effect on VIN)
≈
10V
500nsec
VIN
tR = 10nsec
ID = CDS dv/dt = 1.5pF • (300V/10ns) = 45mA
I • dt
(45mA) • (10ns)
Figure 3 shows the test conditions used for simulating transient voltages. Positive 300V pulses with a pulse width of
500nsec, a rise time of 10nsec, and a duty cycle of 1.0% are
superimposed on the 10VDC line of HVIN. Figures 4a and 4b
are waveforms showing HVIN, VIN and VOUT.
∆VIN =
∆VIN = 45mVPEAK
The low drain-to-source capacitance, CDS = COSS - CRSS =
1.5pF, and high dynamic output impedance, rO = 1.0MΩ,
of the LND1 inherently give the LND1 excellent frequency
response. The LND1 configured as a source follower will
effectively protect high voltage transients on HVIN from affecting VIN. The only paths for transient voltages to get into
VIN are through the 1.5pF CDS or 1.0MΩ rO. Any transient
voltages that pass through will be further attenuated by C2.
The increase in VIN caused by the transient voltage can be
estimated with the equivalent circuit shown in Figure 5.
Negative 300V pulses with a pulse width of 500nsec, a rise
time of 10nsec, and a duty cycle of 1.0% are superimposed
on the 10VDC line of HVIN. The 1N4005 diode is reverse
biased and blocks the negative voltage. Figures 6a and 6b
are waveforms showing HVIN, VIN, and VOUT.
Figure 4a: HVIN and VIN
C2
=
0.01µF
The LND1 with the 1N4005 effectively protects the input of
the 5.0V regulator from positive and negative transient voltages. Theoretical and measured values indicated VIN will
never exceed its maximum rating of 13.5V.
Figure 4b: HVIN and VOUT
HVIN = 310V
HVIN = 310V
VIN = 5.4V
VOUT = 5.1V
10V
10V
Supertex inc.
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
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AN-D17
Figure 6a: HVIN and VIN
Figure 6b: HVIN and VOUT
HVIN = 10V
HVIN = 10V
VIN = 5.4V
VOUT = 5.1V
-300V
-300V
Ripple Rejection Ratio
The ripple rejection ratio, RR, demonstrates the LND150N8’s
capability of filtering AC ripple on the input of HVIN. A 4.0VP-P,
1.0MHz sinusoidal signal was applied to the 5.0V regulator
with and without the LND1. Figure 7 shows the test conditions.
The amount of AC attenuation due to the LND1 can be estimated by the equivalent circuit and equations shown in Figure 8.
Figure 8: Ripple Rejection Calculation
HVIN
Figure 7: Ripple Rejection Test Conditions
HVIN
VIN = HVIN = 9.0VDC + 2.0sin2πftV
f = 1.0MHz
VREG
C2
0.01μF
VIN
VIN
VREG
VOUT
C1
0.01μF
RL
VOUT
C
0.01μF
RL
VIN =
CDS
1.5pF
2sin2πftv
f = 1.0MHz
-
CDS
CDS + C2
C2
0.01μF
VIN
• HVIN
1.5pF
VIN =
• (4.0P-P )
1.5pF + 0.01µF
VIN = 600µVP-P
The ripple rejection ratio was improved by a factor of 1000.
Such a high ripple rejection ratio is particularly useful for
off-line applications. A typical 240VAC off-line application is
shown in Figure 9a.
Measured results are as follows:
Peak-to-peak output AC voltage,
VOUT
RR = 20log
4.0V
Figure 9a: 240VAC Off-Line 5.0V Regulator
IN4005
VOUT with LND1
VOUT without LND1
Conditions
1.3mV, RR = -70dB
2.90V, RR = -2.8dB
No load
1.3mV, RR = -70dB
2.90V, RR = -2.8dB
10KΩ
1.3mV, RR = -70dB
2.90V, RR = -2.8dB
5.0KΩ
Supertex inc.
+
VDRAIN
C3
0.04μF
+
HVIN
-
240VAC
C2
0.01μF
VREG
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
4
VOUT
C1
0.01μF
RL
5k
AN-D17
Figure 9b: VDRAIN and VOUT
While there was a large overshoot voltage without the LND1,
no overshoots were observed in the circuit employing the
LND1. Loads prone to damage by overshoots can be effectively protected by using the LND1.
VDRAIN = 340V
Conclusion
50V
VOUT
Figure 9b shows the voltage waveforms at the drain, VDRAIN,
of the LND1 and the AC voltage at VOUT. There were 290V of
AC ripple observed on VDRAIN with less than 2.0mV of ripples
on VOUT.
C3 is a high voltage holding capacitor. In order to minimize
size and cost, more often than not it is desirable to select
C3 to be as small as possible. The high ripple rejection ratio
helps in achieving a small size of C3 because it allows for
large AC input voltage with negligible AC output voltage.
Power-Up Transient Suppression
The circuits shown in Figures 10a and 10b are powered up
from 0 to 10V in 100nsec. This test demonstrates the stability
of the circuit, the amount of overshoot voltage on VOUT, and
the amount of time required for the output to settle. Large
overshoot voltages on VOUT may damage sensitive loads,
such as CMOS circuits.
The high voltage protected, low power, 5.0V linear regulator
in Figure 1 is a robust, compact, cost effective regulator. It
can operate up to 500VDC, protect against ±500V transients,
and has a maximum quiescent current of 1.0µA. The electrical characteristics of the LND1 allow for the 500V operation and protection. Some examples are proximity controlled
light switches, street lamp control, fax machines, modems,
and power supplies for CMOS ICs in automotive, avionics
and a variety of applications.
Other Application Ideas
The circuit in Figure 1 can be easily modified for higher current capability. The LND1 can be replaced by the Supertex
DN2540N5, which is a 400V, 150mA depletion mode
MOSFET in a TO-220 package. In case the current is low,
and the worst case power dissipation for the DN25 is below
1Watt, the TO-92 version (part #DN2540N3) can be used
to save space and cost. Figure 11 utilizes an op-amp and
an enhancement-mode MOSFET for a much higher output
current capability. Figure 12 is an off-line street lamp control where VSENSE is the input voltage from a light sensing
device.
The test results were:
With LND1
Without LND1
Conditions
VPEAK
tr
VPEAK
tr
0.0V
50µsec
7.6V
1.0µsec
No load
0.0V
60µsec
7.0V
1.0µsec
10KΩ
0.0V
80µsec
6.9V
1.0µsec
5.0KΩ
Supertex inc.
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
5
AN-D17
Figure 10b: Power Up Response without LND1
Figure 10a: Power Up Response with LND1
HVIN
LND1
VIN
C2
0.01μF
HVIN
10V
0V
VOUT
5V
0V
VOUT
REG
C1
0.01μF
VIN
VOUT
REG
C1
0.01μF
RL
VIN 10V
0V
tr = 100nsec
VPEAK
RL
tr = 100nsec
5V
0V
VOUT
tr
tr
Figure 11: High Output Current Linear Regulator
HVIN
C3
D
LND150N3
C2
5.0V
RH5RA50AA
C1
R2
VSET
+
R1
-
VN0340N5
Max406
VOUT = VSET
C4
Figure 12: Off-Line Street Lamp Controller
D2
D1
C3
LND150
+
VIN
-
120VAC
C2
D3
5.0V
RH5RA50AA
VSENSE
C1
VN0640N5
Max406
+
-
R1
Lamp
R3
R2
C4
Supertex inc. does not recommend the use of its products in life support applications, and will not knowingly sell them for use in such applications unless it receives
an adequate “product liability indemnification insurance agreement.” Supertex inc. does not assume responsibility for use of devices described, and limits its liability
to the replacement of the devices determined defective due to workmanship. No responsibility is assumed for possible omissions and inaccuracies. Circuitry and
specifications are subject to change without notice. For the latest product specifications refer to the Supertex inc. (website: http//www.supertex.com)
Supertex inc.
©2012 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited.
011812
1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: 408-222-8888
www.supertex.com
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