Low-current, 60V from battery

[andrewj]

What would be my best option for stepping up a battery source to 60V? The circuit would only draw about 50mA. I was thinking something like a single 9V or a couple of AAs. LiPo's might work too. I've looked at DC-DC step-up modules but these are pretty bulky and overkill for the application. They also have high input voltage requirements >8V. I picked one up from Amazon that makes an audible clicking noise probably because the load is so small. Any ideas?

[Ian.M]

50mA load at 60V is 3W.  Assuming 85% efficiency, that's 3.5W in.  You can forget about the 9V battery or two Alkaline AAs because the output voltage will collapse at high load currents and you'll never get 3.5W out of them.

Heavy duty LiPO/Li-ion or NiMH are an option, but higher voltages will make the design much easier as the input current will be reduced.  I wouldn't want to design for less than 6V in e.g. 6 AA NiMH or two 18650 Li-ion or a 2 cell LiPO pack.
If you have to use primary cells, 4 AA would be marginal, with a service life of about an hour so you, d do better to use 4 C cells or 8 AAs.

Linear Technology's LT1170HV is a possibility but if you don't have prior experience of building switching power supplies, its not likely to go well. 

[NiHaoMike]

A multi cell lipo pack adds balancing issues. One solution could be to use a pack with the balancing circuit built in, but you're probably going to have a hard time finding one of those smaller than a laptop battery. 3.5W isn't unreasonable for a single lithium cell large enough to get a decent runtime. Since the voltage ratio is relatively large, a flyback or tapped boost ("flyboost") topology would probably be your best bet.

What's the end application? About the only ones I can think of would be a portable power supply for condenser microphones or a small tube (pre)amp.