24 volt operation of car amps

[lsm_audio]

hello, this is my first post and have some questions. How can I modify a car amp's power supply so that it can safely operate at 24 volt vehicles? Usually, the p.s. mosfets are irfz44 and switch ic used based on tl494. Can the mosfets handle the double voltage? thanks to all replies...

[Perry Babin]

The mods would depend on the amp. What make/model amp are you using?

The Z44s may hold. They're rated for 55-60v (depending on the datasheet you use). They would see ~2x the input voltage so it would be close to their maximum rating.

The gate drive voltage would have to be limited.

The transformer would almost certainly have to be re-wound. The higher voltage may make it saturate. An alternative may be to increase the operating frequency. The ratio would also likely be too high and would cause excessive rail voltage. Even if the power supply is regulated, the excessive winding ratio (for the 24v input) would likely cause the filter capacitors on the primary side of the supply to overheat when the amp is driven hard.

The primary side capacitors would need to be replaced if they're not rated for 35v or more.

[lsm_audio]

thanks very much Perry for the details, actually I am thinking of building a 24v-12v voltage regulator based on tl494 instead of modifying the power supply of the car amp. I do repair works on car amps here in the Philippines and our shop also installs these amps on 24 volt operated 'jeepneys' and we just use 24v-12v converter which is just linear designed and of course bulky.

[Andrew Eckhardt]

I'd say a z44 is going to fail. Any little overshoot at all and you're over the edge with that part. I'd start with a 540 or something. I'd also recommend modifying the converter in the amp rather than adding a converter, if you're already looking at building a converter. You'll have to double the turns on the primary and replace the input filter caps. Make sure the converter IC supply section is able to handle 24 volts too. Should be fun, and much higher performance than adding a converter.

[lsm_audio]

thanks Andrew for your suggestions, ok I'll be doing some mods first

[Eva]

Some hints:

- 100V MOSFET for the push-pull PSU, adjusting gate resistors and dead time to keep resonant operation
- Double the primary turns with half the amount of magnet wires
- Adjust RC snubbers on primary windings
- A 15V regulator inserted where power for the TL494/SG3535 and other stuff is taken from the main +B rail.

[Andrew Eckhardt]

Yeah the 494 can handle up to 41 volts but the driver stage should probably be held to something under 15V for low power FET on resistance but not too high gate charge. You'd probably want a good schematic of the existing circuit to start.

[lsm_audio]

thanks Eva for the tips I think a 7812 regulator would fit in for the switch IC

[Eva]

The gates of the MOSFET can handle 20V and the control IC and gate buffers (if any) usually drop 1V to 2V, so 15V is better (to get 13-14V at the gates, the most usual voltage in anything but car amps).

Remember to replace capacitors with not enough voltage rating. The input electrolytics should be 35V. 24V systems can produce up to 30V when the alternator is working.

Check this heavy duty 100V MOSFET:
http://www.irf.com/product-info/data...fb4310zpbf.pdf