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Product Guides and Tutorials

Power Pulse ModulatorPower Pulse Modulators


Our range of Power Pulse Modulators have been designed to be as versatile and tolerant as possible so that they can be used in all sorts of ways. However, if for some reason your Power Pulse Modulator has been damaged or is malfunctioning, this guide will help you to determine the cause and give you steps to remedy the problem.

When removing thru-hole components, we recommend cutting off the component before trying to desolder them. The solder pads are dual layer PTH with double thickness copper and may need quite a hot soldering iron (about 350 C). After cutting the component off, melt the solder of one pad, then pull out the leg with tweezers. After removing the legs, remove remaining solder with a desoldering pump.

For removing surface mount parts we suggest using a SMD reworking heat gun, but alternatively you can use a soldering iron. There are lots of guides on how to do this online.


Possible Causes


Output Stuck on / Green LED continuously lit and not changing with duty setting The most common reason for this would be due to a failiure of the main transistor. This can be cause by excessive current, or overheating.

First determine if the fault is with the transistor or elsewhere in the circuit. To do this, remove the jumper link labeled INVERT and then power on the device (without a load). Ih the green LED is still lit, then you will need to replace the transistor with an FGA60N60.

If the LED goes off when you remove the jumper link, then the problem is with the control circuit and will need further tests.


Troubleshooting for older models




Possible Causes


Overheating or blown TVS (SP1) This component is used to protect the rest of the circuit from large voltage transients. This component will overheat if there are continuous large voltage transients that are above the secondary switching voltage rating of the power pulse modulator. You will need to take measures to reduce the transients. This may be as simple as adjusting the frequency. For other methods, please see the page about driving inductive loads. If the component marked SP1 has been damaged, it should be replaced with another TVS. For the PWM-OCB, and PWM-OCX, use the 1.5KE56CA, for the PWM-OCBI and PWM-OCXI, use the 1.5KE440CA

Overheating or blown diode (D1 or D2)

If you mistakenly connect the power to your device with the wrong polarity and have not used a suitable fuse, either of these diodes could fail. Large transients on the power supply input, or an input supply above the rated value could also lead to overheating of these components. Replace the diodes if needed, and ensure you follow all suggestions in the datasheet for operating the device within its defined parameters. D1 is a 1N5363B, and D2 is a 1N5819.

Overheating power capacitor (C2)

The power supply or connecting cables used have a high impedance and can not deliver fast current pulses to the device. Add more capacitance to the input terminals V+ and GND as shown in the datasheet. Use shorter, and thicker cables to connect between the PSU and the Power Pulse Modulator. See the page on power supply considerations for more details.

Overheating or blown power transistor (T1)

Too much current for the selected frequency. Reduce the duty and/or frequency setting. Increase the load impedance. If you need to replace the transistor, for the OCB and OCX use a STP30NF10, or for the OCBI and OCXI use a IRGB4061DPBF
Green LED stuck on and output is stuck on 100% Blown transistor or TVS (see details above).

Damaged control circuit

Remove the jumper link "INV" near the transistor. Power on the device (no load attached) and check the green LED. If it is still illuminated, then the problem is with the power control circuitry such as the transistor or TVS. If the LED is not lit, the problem is with the control circuit.

LED still lit: Disconnect any load, remove SP1 then power on the device to see if the output is working again. If it is working replace SP1 with a new part. If the output is still stuck on, replace the  zener diode D5, and/or the transistor too.

LED not lit: Replace all three IC's. (NE555, LM393, TC4428)

Diodes D1 and/or D2 burned out Input voltage applied in reverse, or excessively high input voltage applied.

Remove the damaged diodes and try applying the correct input supply to the device (with no load attached). If the device is now operational, just replace both diodes. D1 is a 1N5363B. D2 is a 1N5819. If it is still not operating, also replace U1 (12V Regulator). You may also need to replace the tall capacitor C2 (330uF electrolytic) is reverse input was applied. You should always use a fuse at the input as this can prevent or reduce damage.

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Comments and questions for PWM Troubleshooting

The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.