looking for a low size and cheap DC/DC negative inverter

[ali_asadzadeh]

Hi,
I want to know if you know something for generating -12V from 5V like the jelly-bean MC34063 in SOT23 package,for powering op-amps, I need at most 100ma current. do we have chinese parts? I need it to be sub 0.1$

[i_am_fubar]

I imagine a charge pump could do this for minimal cost as there's no inductor requirement.

What sort of volume? Not going to get a single component solution for that cost in any low volume.

[ali_asadzadeh]

Can a charge pump supply 100ma!?

[Yansi]

Charge pumps are the shittiest way of doing things.

Use for example AOZ1282CI or any other cheap buck converter for it. There is a metric shit ton of these available. And yes, they are cheap.

[ali_asadzadeh]

Thanks Yansi for the hint, I want to generate -10V, this part is a buck! how can it be done?

[ali_asadzadeh]

Thanks blueskull, can it give 100ma? Also what's the size of the cap that couple into the reverse diode?

[MagicSmoker]

Thanks blueskull, can it give 100ma? Also what's the size of the cap that couple into the reverse diode?

It's safe to say you didn't even bother to download the MT3540 datasheet... 

[Yansi]

Blueskull: Wtf?

Almost every buck converter can be used as an inverting converter. Because it doesn't matter, if it makes   3V from 5V, or  -5V from 5V. Either way the output voltage is lower, that input one. (Input voltage is the Vin+Vout, output just Vout). So I have correctly suggested a AOZ1282 for the job.

Just connect the input voltage to input +V terminal,  the output V+ of the buck connect to input and output GND, then you get the negative voltage from the former GND of the buck converter. (In fact, this way the buck converter becomes wired as a textbook inverter).

[ali_asadzadeh]

It's safe to say you didn't even bother to download the MT3540 datasheet... 

I have and it's a boost cnvertor! I think blueskull has some points and i think it can be done in this way too.

Almost every buck converter can be used as an inverting converter. Because it doesn't matter, if it makes   3V from 5V, or  -5V from 5V. Either way the output voltage is lower, that input one. (Input voltage is the Vin+Vout, output just Vout). So I have correctly suggested a AOZ1282 for the job.

Just connect the input voltage to input +V terminal,  the output V+ of the buck connect to input and output GND, then you get the negative voltage from the former GND of the buck converter. (In fact, this way the buck converter becomes wired as a textbook inverter).

I do not get it fully, would you explain with a circuit diagram!?

[ali_asadzadeh]

Thanks

[Yansi]

Blueskull: Wtf?

Because I like to do it this way. In addition I get a free +12V. This is very common in signal circuitry where a bipolar OPAMP supply needs to be generated from a single 3.3V or 5V.

I do not like this configuration and do not suggest using it.  A lot of ICs do not like to switch into capacitive loads like this and will trip the OCP. Also I'd say this produces likely more EMI, due to higher di/dt in the charge pump circuit (no di/dt limiting element at transistor switch on). Output regulation is also worse (may not be an actual problem though).