NCP1055: Simple, 3 W, Non-isolated Bias Supply

DN06053/D
Design Note – DN06053/D
Simple, 3 W, Non-isolated Bias Supply
Device
Application
Input Voltage
Output Power
Topology
I/O Isolation
NCP1055
Non-isolated Logic
Bias Supply
90 to 300 Vac
100 to 450 Vdc
3 W Nominal
Buck
None
Other Specification
Output
Output Voltage
Ripple
Nominal Current
Max Current
Min Current
12 to 15 Vdc
Less than 2%
50 to 200 mA
250 mA
Zero
No
65%
Yes
0 to +50˚C
Convection – no specific
orientation
None
PFC (Yes/No)
Minimum Efficiency
Inrush Limiting / Fuse
Operating Temp. Range
Cooling Method /
Supply Orientation
Signal Level Control
Circuit Description
This circuit is a very simple buck regulator
configured for a non-input isolated, 3 W bias power
supply for appliances, industrial electronic
equipment or the primary circuitry of a larger power
supply. This specific example is a 15 Vdc at 75 mA
with a 125 mA output resistively lowered to 12 Vdc
for a small, optional dc cooling fan. If desired, the
fan output can be eliminated and the full 200 mA
with a 250 mA surge can be provided by the 15 Vdc
output. By choosing the correct zener voltage for
Z1, most voltages from 5 V to over 28 V can be
configured.
The key to the simple circuitry is the use of ON
Semiconductor’s NCP1055 monolithic controller
with an internal 700 V MOSFET. The controller
works as a gated oscillator which shuts off when the
sense input level on pin 2 exceeds about 4.7 volts.
The output voltage is sensed using a “bootstrap”
circuit composed of R1, D3, and C4 which allows
accurate sensing despite having the ground
reference at a switching node (cathode of D4).
By using the gated oscillator approach instead of
March 2009, Rev. 0
conventional, analog PWM control, maximum
simplicity is achieved without stability or control loop
issues. The amplitude of the output ripple can be
controlled by the inductance value of L1 and the
inherent ESR of output capacitor C5. For voltages
less than 9 Vdc it may be necessary to slightly
increase both the inductance and capacitance
values of these components.
Key Features
• Ultra-simple circuit with excellent output
regulation
• Inherent over current/over temperature protection
in NCP1055
• Off-the-shelf components
• Configurable for most output voltages greater
than 5 Vdc
www.onsemi.com
1
DN06053/D
Schematic1
Input 100 - 450 Vdc
or 90 - 300 Vac
_
+
200 mA Bias Supply
D1
1N4007
F1
0.5A
250Vac
U1
D2
C1
15uF
400V
NCP1055
(SOT223)
3
4
2
1
1N5240B
(10V)
Z1
1N4148
C3
C4
100pF
0.22
25V
C2
10uF
16V
D3
R1
MUR160
2K
+15V
Logic Vcc
R2
L1
15V Vcc
22, 1/2W
+12V Fan
(option)
1.8mH
D4
MUR160
C5
330uF
25V
Z2
1N4746A
(18V)
Return
Notes:
1. L1 is Coilcraft RFB1010-182L or equivalent (1.8 mH, 400 mA).
2. Vout set by Z1 zener voltage = Vz1 + 5.2 volts (approximately).
3. D1 unnecessary if input is dc.
4. R2 limits voltage for optional equipment fan to 12 Vdc.
5. Z2 is for output OV protection.
6. Crossed lines on schematic are not connected.
Bibliography and References
ƒ Data sheet NCP1055: Monolithic High Voltage Gated Oscillator Power Switching Regulator
ƒ Application note AND8098: Low-Cost 100 mA High-Voltage Buck and Buck-Boost Using NCP1052
1
© 2009 ON Semiconductor.
Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor
does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to
assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated
with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its
products at any time, without notice.
Design note created by Frank Cathell, e-mail: [email protected]
March 2009, Rev. 0
www.onsemi.com
2